There are a wide variety of fastening or mounting systems to form structural connections for joining or mounting two or more mechanical or structural components together. Of these systems, they can be generally classified as either of the temporary-type which can include the use of screw fasteners, snap fit arrangements, and clamping mechanisms, or of the permanent-type which include brazed, welded and riveted joints. The latter type of mounting systems typically require more extensive labor than the former, such as when comparing welding versus the use of a screw fasteners or snap fit arrangements. Thus, in many instances, the use of the temporary-type of mounting systems are preferred. This is particularly true in the assembly operations for automobiles where minimizing assembly time can be of paramount importance.
In the automotive field where housings can be utilized to contain sensitive electrical components for mounting them in the vehicle, such as controllers having sensors for activating various safety devices (e.g., airbags) in the automobile once a predetermined crash condition is sensed, secure and rigid mounting of the housing to the vehicle frame or chassis is critical. In view of the earlier-mentioned need for fast assembly time, the mounting systems for controller housings in automobiles have focused on the temporary-type of mounting previously described, in particular of the bolt or screw fastener type. This additionally provides the advantage of disassembly to allow for servicing or replacing of components contained within the housing when necessary. In particular, housings for airbag controllers are typically mounted utilizing only a bolted attachment between the housing and the vehicle chassis, such as to the floor under the auto mobile seat. Such bolted mounting systems utilize up to six bolts to obtain the desired rigidity and strength in the mounting of the housing to the chassis.
The use of large numbers of bolt or screw fasteners to attach or mount the housing to the frame of the car increases costs for producing and installing the housing into an automobile. With mounting systems requiring large numbers of tightly torqued bolts to properly mount the housing, more parts must be produced and the housing must be provided with portions having clearance holes for receiving the fastener therethrough which, depending on the number of fasteners utilized, can undesirably increase the size of the housing. In addition, the time required for inserting and torquing the bolts to mount the housing to the vehicle chassis goes up with each additional bolt utilized. Another consideration for an assembly exclusively employing bolts is that the strength of the mounting depends to a great extent on the initial loading and stress placed on the bolt by the assembly torque. Thus, where safety concerns are paramount, very small bolts or screws are dangerous to use because it is easy to overload the bolt or screw in assembly and actually twist it off. Thus, larger bolts which can take greater assembly torque loads would be desirable; however, larger bolts necessarily and undesirably increase the size of the bolted-only mounting systems. Accordingly, there is a need for a mounting system for housings which reduces the number of parts needed for assembly and also reduces the assembly time required for mounting the housing to the vehicle frame. Specifically, a mounting system which does not rely so heavily on bolted connections would be preferred so as to be able to reduce the number of bolts employed in the system.
In a effort to address the above needs of automobile manufacturers as to reducing parts and assembly time, it has been proposed to use snap fit arrangements in conjunction with bolts to lower their number. Snap fits typically will include an extension part on the housing which is pushed into a tight fitting opening in the vehicle chassis so that the extension deforms as it is inserted and rebounds or snaps back to its original undeformed configuration once cleared through the frame opening so as to provide a snap fit between the two. With snap fit arrangements, it has been found that the housing will tend to rattle, particularly after prolonged exposure to the high vibration environment encountered when used in automobiles. Any rattling is not acceptable in the automobile industry, especially where the housing is to be used to mount electronic components to the vehicle chassis, such as the above-described airbag controller. Rapid vibration or rattling of the housing when used to contain a controller can cause serious problems in the electronic equipment utilized and lead to malfunctions of any operating systems they may control. In addition, automobile manufacturers do not want high insertion forces for assembly purposes, such as would be necessary in a design of a snap fit arrangement that would provide sufficient strength and rigidity for securely mounting the housing to the vehicle chassis without shifting or rattling relative thereto. Thus, there is a need for a mounting system for a housing such as that for vehicle electronic components, e.g., airbag controllers, which secures the housing to the vehicle chassis without producing looseness or rattling of the housing even after prolonged exposure to high vibration environments and which has low insertion forces for ease of assembly thereof. In addition and as previously discussed, such a mounting system should utilize a minimum number of parts to lower manufacturing and assembly costs for the housing mounting system.